Practically all in vitro mechanical investigations of blood vessels from hypertensive animals have utilized the aorta or other relatively large arteries, and there is a paucity of specific information about the small arteries. These small vessels participate in the control of peripheral resistance and ultimately all pertinent questions regarding their involvement in hypertension must be answered by direct measurement. We propose to study intact cylindrical segments of mesenteric vessels having lumen diameters of 75-300 micron m from the spontaneously hypertensive rat (SHR) and its normotensive control, the Wistar Kyoto rat (WKY). Measurements will be made of their: geometric characteristics (e.g., wall/lumen ratio); mechanical properties (e.g. active and resting tension-length relationships); contractile behavior of the vessel wall and smooth muscle cells (e.g. dynamic responses to step, circumferential length changes); morphology using electron- and light-microscopy (e.g. amount of smooth muscle in the walls and cell size). Animals of different ages will be used to determine: whether observed changes in properties occur before or after the establishment of hypertension, whether changes occur during the maintenance of hypertension; and, whether changes may be reversed by pharmacologic treatment of the hypertension. This study will: 1) afford data not now available on small arteries, and smooth muscle cell physiology; 2) document functional changes of the artery wall in the course of developing, maintained and treated hypertension; 3) permit the determination of physical parameters for modelling of the normotensive and hypertensive vessel wall; 4) demonstrate possible mechanisms by which the smooth muscle cell contractile force may be transmitted to the wall of the artery; 5) possibly have long-range implications in the treatment of human essential hypertension. BIBLIOGRAPHIC REFERENCES: Halpern, W. and R.L. Moss. Elastic modulus and stress relationships in stretched and shortened frog sartorii. Am. J. Physiol. 230:205-210, 1976. Mulvany, M.J. and W. Halpern. Mechanical properties of vascular smooth muscle cells in situ. Nature 260:617-619, 1976.